Disable editing of multiple objects in Blender 2.8
From your comments I can see your problem is due to having other objects selected and not knowing about them. Not a real solution for your problem but, whenever I'm modelling with several objects, as a good practice I always tap A twice to deselect everything before selecting the object (I use the Blender 2.79 hotkeys). There are many advantages in being able to go to edit mode with multiple objects and I'm sure you will soon make use of them as well.

Update: For Blender 2.8 it's Alt+A to deselect anything.